The use of a sterilizing or biocidal gas or a mixture of gases as a sterilization medium is well established in the prior art. Such gaseous atmospheres are highly effective in de-activating and destroying viable micro-organisms and insects as well as life-cycle forms through which such organisms evolve.
Gaseous sterilization systems of the type contemplated and utilized in the present invention are "non-destructive". Autoclaving, caustics, corrosive agents, and other deleterious agents and techniques are avoided. Accordingly, the procedures of the invention are specially adapted to the treatment of perishable substances such as foodstuffs, agricultural products, and pharmaceuticals as well as the sterilization of intricate and costly hospital equipment including surgical instruments and apparatus.
Alkylene oxides are extensively used as non-corrosive gaseous sterilizing agents; the most commonly used are ethylene oxide and propylene oxide. These compounds destroy many types of objectionable organisms, remain gaseous at relatively low temperatures, are non-corrosive, and are essentially non-destructive with respect to sensitive and delicate metals and many other materials including plastics, rubber, adhesives, comestibles, and drugs. Alkylene oxides are ordinarily diluted with an inert gas such as a halogenated hydrocarbon or with carbon dioxide to eliminate flammability. A commercially available mixture consisting of about 12% by weight of ethylene oxide mixed with 88% by weight of a halogenated hydrocarbon such as dichloro difluoromethane (Freon 12) is a preferred formulation. Other "inert" halogenated hydrocarbons marketed under the trademarks FREONS, UCONS, and GENETRONS may be used as diluents for the ethylene oxide to obviate flammability and to prevent the development of explosive atmospheres.
Until relatively recently, the sterilization technique adapted has been to place the articles or materials to be treated in a tank or sterilization chamber and then to introduce a prescribed composition of sterilant into the chamber at controlled temperatures and pressures. After a predetermined, selectible dwell time, the sterilant gas was pumped from the chamber and discarded into the atmosphere. Finally, the chamber was swept with filtered air. No effort was made to reclaim the sterilant mixtures for re-use.
However, with the marked increased in materials cost, and with recognition of ecological problems posed by indiscriminate discharge of the ethylene oxide and the halogenated hydrocarbons into the air, new techniques have been devised. After use, the gaseous mixture is recovered to be used again. In the new processes, the concentrations of components in the gaseous mixture are readjusted prior to re-use. An example of the re-use of sterilizing gas (steam) through recovery, condensation, and recyclization in a closed system is described in Skaller U.S. Pat. No. 3,361,517. Satas U.S. Pat. No. 3,372,980 describes ethylene oxide recyclization in a gaseous sterilization system and suggests the periodic refortification of the gas mixture by addition of pure ethylene oxide. Ernst U.S. Pat. No. 3,549,312 also describes recovery and condensation of a sterilizing gas for re-use, and maintenance of the desired mixture through addition of the "inert" diluent, as required to reconstitute the mixture to the desired concentrational composition.
Notwithstanding extensive research and development in the field of gaseous sterilization, particularly in recovery and re-use of the sterilizing agents, no completely satisfactory apparatus or process has heretofore been achieved. Each of the prior art procedures suffers from deficiencies or shortcomings which have impaired general usefulness and have precluded adoption by the industry. It is, accordingly, the aim of the present invention to provide an improved process and apparatus whereby the recovery and re-use of sterilization gas atmospheres may be safely, effectively, and economically carried out.